System and method for fracturing a hydrocarbon producing formation

ABSTRACT

A system and method for fracturing a hydrocarbon producing formation in which a tool assembly is inserted in a wellbore adjacent the formation, and fracturing fluid is introduced into the annulus between the tool assembly and the wellbore and flows to the formation.

BACKGROUND

[0001] This invention relates to a system and method for fracturing ahydrocarbon producing formation with a fracturing system located in awellbore adjacent the formation.

[0002] It is often necessary to selectively treat hydrocarbon zones, orformations, to extract hydrocarbons from the formation while isolatingthe formation from other intervals in a wellbore. Such treatmentsinclude perforating the well casing adjacent the formation andintroducing a fracturing fluid through tubing into a tool assembly inthe casing, and to a ported sub, or the like, connected in the toolassembly. The fluid discharges from the ported sub at a relatively highpressure and passes through the perforations in the well casing and intothe formation to fracture it and promote the production of thehydrocarbons such as oil and/or gas. Often, the formation is isolated bysetting packers above and below the ported sub to seal the zone duringthe fracturing operation.

[0003] However, these types of techniques are not without problems. Forexample, the use of a packer above the ported sub causes a high pressuredifferential between the formation and the area of the well above thepacker, which may cause the packer to unset during operation, possiblyresulting in unsuccessful fracture treatment, tool damage, and loss ofwell control.

[0004] Also, the introduction of fracturing fluid through the tubing andtool assembly creates additional problems, not the least significant ofwhich is the fluid friction created by the passage of the fluid, whichlead to mechanical failure of both the tubing and tool assembly. Thus,the diameter of the tubing must be optimized to allow maximum fluid rateand pressure subject to the constraints of weight, storage, and cost oflarge-diameter tubing.

[0005] Therefore, what is needed is a fracturing system and method thateliminates the above problems.

BRIEF DESCRIPTION OF THE DRAWING

[0006] The drawing is partial sectional/partial diagrammatic view of asystem according to an embodiment of the invention.

DETAILED DESCRIPTION

[0007] Referring to the drawing, a tool assembly is referred to, ingeneral, by the reference numeral 10 and is shown installed in a casing12 disposed in a well. The casing 12 intersects a ground formation Fwhich typically contains hydrocarbon fluids, and the tool assembly 10 islowered to a predetermined depth in the casing 12 near the formation Fand defines, with the casing 12, an annulus 14.

[0008] A packer 16 and a jet perforating sub 18 are connected in thetool assembly 10 in any conventional manner with the packer 16 extendingdownstream, or below, the sub 18. Although not shown in detail, it isunderstood that the packer 16 is adapted to form a seal across theannulus 14 and, as such, includes at least one packer element, which canbe in the form of a torus fabricated from an expandable materialsurrounding a mandrel, and held in place in any conventional manner. Thepacker 16 also includes a mechanism or mechanisms to anchor the packer16 in a position adjacent or near the formation F, after which thepacker elements are expanded against the casing 12 to seal against axialfluid flow through the annulus 14 downstream of the packer 16. Thepacker 16 can be of any conventional design including those disclosed inassignee's U.S. Pat. Nos. 4,524,825, 4,590,995, 4,627,491, 4,697,640,4,962,815, 5,701,954, and 6,056,052, all of which are incorporated intheir entirety herein by reference.

[0009] The sub 18 contains a plurality of jet openings for dischargingperforating fluid and fracturing fluid through the casing 12, throughany cement between the casing 12 and the well, and into the formation F.The sub 18 can be of any conventional design including those disclosedin assignee's U.S. Pat. Nos. 5,499,678 and No. 5,765,642, both of whichare incorporated in their entirety herein by reference.

[0010] Several other components, such as a blast joint, a centralizer, arelease joint, and the like, can be provided in the tool assembly 10upstream, or above, the sub 18 and between the sub 18 and a connector20. Since these components are conventional, they are not shown, norwill they be described in detail. The connector 20 is connected to asection of coiled or jointed tubing 22 which is lowered in the well fromthe ground surface to locate the packer 16 and the sub 18 at a depth inthe well in the vicinity of the formation F.

[0011] After the packer 16 and the sub 18 are positioned in the casing12 in the above manner, they are set in a conventional manner so thatthe above-mentioned packer elements and anchor mechanisms engage theinner surface of the casing 12 to form a seal, as described above.

[0012] An abrasive fluid is then pumped from the ground surface, at arelatively high pressure, through the tubing 22. The abrasive fluid caninclude an abrasive particulate material, such as sand, suspended in aliquid, such as water, or chemically-treated water. The abrasive fluidflows to the sub 18 and discharges through the jet openings in the sub18 and into the annulus 14 at a very high pressure and impacts againstthe inner surface of the casing 12 to form perforations 12 a through thecasing 12. It is understood that any cement extending between the casing12 and the well will also be perforated in the above manner, and theperforations 12 a thus created may penetrate into the formation F aswell as forming indentation therein.

[0013] The flow of the abrasive fluid is then terminated, and the toolassembly 10 is cleaned in any conventional manner, such as by pumpingcleaning fluid down the annulus 14 so that the cleaning fluid enters thelower portion of the tool assembly 10 and flows in a reverse directionupstream through the tool assembly 10, including the sub 18, and thetubing 22. In this context, it is understood that the sub 18 can beprovided with a valve (not shown) that permits the flow of the abrasivefluid downstream through the sub and the jet openings as describedabove, but prevents the cleaning fluid that flows through the sub 18 inthe opposite, or reverse, direction to discharge through the jetopenings.

[0014] Fracturing is then commenced by pumping a conventional fracturingfluid, at a relatively high pressure, from ground surface down theannulus 14 in any conventional manner until the fracturing fluidpenetrates the formation F, and, more particularly, the above-mentionedindentations in the formation F, to fracture the formation F andfacilitate the extraction of oil and/or gas. The seal formed by thepacker 16 permits this flow upstream of its location but prevents anyfluid flow downstream.

[0015] Upon completion of this fracturing treatment, the flow of thefracturing fluid is terminated and the tool assembly 10 is again cleanedby pumping cleaning fluid down the annulus 14 so that the fluid entersthe lower portion of the tool assembly 10 and flows upstream through thetool assembly 10, including the sub 18, and the tubing 22 in the mannerdescribed above.

[0016] Once the above operation is completed, the packer 16 can bereleased from its set position as described above, and the tubing 22,and therefore the tool assembly 10, can be moved axially in the casing12 to another formation where the above method can be repeated. In thiscontext, it is understood that the tool assembly 10 can include acirculation port to allow fluid circulation from the annulus 14 to theinterior of the tool assembly 10 and the tubing 22 to promote thecleaning of the tool assembly 10. The preferred method for treatingmultiple formations is to sequentially treat the formations intersectedby the well beginning with the lowest formation.

[0017] Flowing the fracturing fluid down the annulus and eliminating theuse of an upper packer located above the sub 18 avoids theabove-mentioned problems associated with introducing the fracturingfluid through a tubing and tool assembly utilizing an upper packer.

Variations and Equivalents

[0018] It is understood that variations may be made in the foregoingwithout departing from the scope of the inventions. For example, thetype of packer and jet perforating sub can be varied. Also, the abrasivefluid, after perforating the casing, can flow to the formation F at veryhigh pressure and form indentations, in the form of openings, bores,cracks, or the like, in the formation F to assist in the fracturingprocess. Further, the system described above is not limited to verticalwells, but is equally applicable to wells that deviate from thevertical. Moreover, the perforations in the casing can be formed byother methods, such as by using explosive charges. Still further,spatial references, such as “above”, “below”, “upper”, “lower”, “outer”,“over”, “between”, “inner”, and “vertical” are for the purpose ofillustration only and do not limit the specific orientation or locationof the structure or flow paths described above.

[0019] Although only a few exemplary embodiments of this invention havebeen described in detail above, those skilled in the art will readilyappreciate that many other modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention as defined inthe following claims.

1-21. (canceled)
 22. A method for fracturing a formation adjacent a wellhaving a casing disposed therein, comprising: inserting a tool assemblyin the casing to form an annulus between the tool assembly and thecasing, the tool assembly including a plurality of jet openings; forminga seal across the annulus below the jet openings to prevent fluid flowin the annulus downstream of the seal; passing an abrasive fluid intothe tool assembly for discharge through the jet openings and towards thecasing to form perforations in the casing; introducing a fracturingfluid into the annulus above the seal for flowing through theperforations and into the formation for fracturing the formation; andintroducing a cleaning fluid into the annulus for passing into the toolassembly for cleaning same.
 23. The method of claim 22 wherein thecleaning fluid is introduced after the step of passing and before thestep of introducing the fracturing fluid.
 24. The method of claim 22wherein the cleaning fluid is introduced after the step of introducingthe fracturing fluid.
 25. The method of claim 22 wherein the cleaningfluid is introduced after the step of passing and before the step ofintroducing the fracturing fluid; and further comprising introducingadditional cleaning fluid into the annulus after the step of introducingthe fracturing fluid.
 26. The method of claim 22 wherein the cleaningfluid passes into the tool assembly through circulation ports formed inthe lower portion of the tool assembly.
 27. The method of claim 22wherein the step of forming the seal comprises connecting a packer tothe tool assembly, and setting the packer.
 28. The method of claim 22wherein the step of passing the abrasive fluid comprises the steps of:connecting a sub to the tool assembly, the sub having the jet openings;introducing the abrasive fluid to the sub; and discharging the abrasivefluid through the jet openings towards the casing.
 29. The method ofclaim 22 further comprising: releasing the seal; moving the toolassembly to another location in the well; forming another seal acrossthe annulus below the jet openings to prevent fluid flow in the annulusdownstream of the seal; passing additional abrasive fluid through thetool assembly and towards the casing to form perforations in the casing;introducing additional fracturing fluid into the annulus for flowingthrough the perforations and into the formation at the new location forfracturing the formation; and introducing cleaning fluid into theannulus for passing into the tool assembly for cleaning same.
 30. Asystem for fracturing a formation adjacent a well having a casingdisposed therein, the system comprising: a tool assembly adapted to belocated in the casing to form an annulus between the tool assembly andthe casing; a seal disposed on the tool assembly and adapted to extendacross the annulus to prevent fluid flow in the annulus downstream ofthe seal; means for passing an abrasive fluid through the tool assemblyand towards the casing for forming perforations through the casing;means for introducing a fracturing fluid into the annulus for flowingthrough the perforations and into the formation for fracturing theformation; and means for introducing a cleaning fluid into the annulusfor passage through the tool assembly for cleaning the tool assembly.31. The system of claim 30 further comprising ports provided in thelower portion of the tool assembly for receiving the cleaning fluid. 32.The system of claim 30 wherein the tool assembly comprises a sub havingjet openings through which the abrasive fluid is discharged.
 33. Thesystem of claim 30 wherein the seal is a packer.
 34. The system of claim33 wherein the packer can be set to form the seal and can be released topermit the tool assembly to be moved to another location in the wellafter which it is reset.